Li-ion battery is a kind of secondary battery (rechargeable battery), which operates based on movements of lithium ions between the positive electrode and negative electrode. During the charging-discharging process, Li+ is intercalated and dis-intercalated back and forth between the two electrodes: when charging, Li+ is dis-intercalated from the positive electrode, goes through the electrolyte and is intercalated into the negative electrode, then the negative electrode is at a Li-rich state; it is on the contrary when discharging. A battery usually adopts a lithium containing material as the electrode, which is a representative of modern high performance battery. As long as Li-ion battery is commercialized, due to its advantages such as high energy density, high voltage, low self-discharging rate, light weight and the like, its commercialization development is rapid, for example, it is widely applied in the field of electronic products such as cellphone, laptop, digital camera, mobile DVD, video camera, MP3 and the like, as well as the field of transportation means such as electric bicycle, electric vehicle and the like. In addition, applying Li-ion battery can save space, reduce cost as well as solve the problem that the capacities of batteries must be matched with each other when being connected in series, so as to increase energy density, improve reliability when in use, moreover, the Li-ion battery has no memory effect, which will not pollute the environment. As a new secondary battery, with continuous improvements on its performance such as cycling performance, low-temperature performance, service life and safety etc., the Li-ion battery may possibly be widely applied in the field of military equipment either.
At present, the requirements on energy is higher and higher, a single battery cannot provide sufficient energy, a solution is provided to connect a plurality of batteries in series or in parallel to form a battery pack so as to solve the above problem, however, as a result of the difference and quality reasons among single batteries, a single battery or several batteries in the battery pack may not be continuously used due to the service life, performance, safety and so on, such a situation may cause that the whole battery pack cannot keep operating, which has to be repaired or replaced or even discarded and recycled.